Play with Radii
Geometry
Level
2
Three circles with radii 4,5 and 9 have the same center. If x% of the area of the largest circle lies between the other two circles, what is x to the nearest integer?
22
33
8
11
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1 solution
The formula of the area of the circle is A=(pi)r r: therefore, the area of the largest circle is [81(pi)] for the 2nd largest is [25(pi)] for the smallest is [16(pi)] In solving, I can relate this to the formula: P=B R I can place 81(pi) as the base: P=81(pi) R And I will deduct 16(pi) from 25(pi) coz the problem asks for the area between the two other circles. Then the result is 9(pi), therefore I can put in the formula as 9(pi)=81(pi) x% x%=0.11111111... The problem asks that, what is x to the nearest integer? therefore, the answer is 11